of the Yellow-stone and Missouri rivers, there is a
high plain, which extends three miles in width, and seven or eight miles
in length; and which Captain Lewis says might be rendered a very
advantageous station for a trading establishment.

Beyond this place, the hills were rough and high, and almost overhung
the river. As the voyagers advanced, the low grounds were fertile and
extensive, with but little timber, and that cotton-wood. On the 3d of
May, they reached the mouth of a river, which; from the unusual number
of porcupines that were seen near it, they called _Porcupine river_. For
several days after this, they continued their progress without much
interruption. In many places the river was, at least, half a mile wide.
During their excursions on the shore, in pursuit of food, they
encountered many perils in shooting at bears. Some of these were of vast
size and strength: one of them weighed nearly six hundred pounds, and
measured eight feet seven inches and a half, from the nose to the
extremity of the hind feet.

Beyond the _Muscle-shell river_, which the voyagers reached on the 21st,
the shores of the Missouri were abrupt and bold, and composed of a black
and yellow clay.

After a navigation of two months, and a progress of more than a thousand
miles from their winter camp, the party became considerably embarrassed,
at the conflux of two rivers, which were, apparently, of equal
magnitude. It was important for them to decide which of the streams in
question was the true Missouri; because the river, which it was their
object to ascend, was described to be at no great distance from the head
waters, running, from the opposite side of the Rocky Mountains, towards
the Pacific ocean. Two canoes, with three men, were consequently
dispatched, to survey each of these doubtful streams; and parties were
sent out by land, to discover, if possible, from the rising grounds, the
distant bearings of the lofty ranges of mountains, which were
conspicuous in the west; and some of which, though it was now the month
of June, were covered with snow. Hence, there was no doubt of their
vicinity to the great central ridge of American mountains; but the
direction of the rivers just mentioned, could not be distinguished to
any considerable distance. Of the two, the one coming from the north,
had the brown colour and thick appearance of the Missouri; while the
southern river had a rapid current, a pebbly bed, and transparent
water, as if